Methods and apparatus for controlling power in vapor jet vacuum pumps

ABSTRACT

Methods and apparatus for controlling power supplied to vapor jet vacuum pumps are provided. A vapor jet vacuum pumping system includes a vapor jet pump having an inlet port, an exhaust port, a jet assembly and an boiler, the boiler including a heater, and a power controller for automatically controlling power supplied to the heater in response to at least one control parameter. The power may be controlled in response to a programmed sequence, to a sensed pressure in a process chamber, to control signals from a process control system, or to combinations of these control parameters.

FIELD OF THE INVENTION

[0001] This invention relates to vapor jet vacuum pumps and, moreparticularly, to methods and apparatus for reducing power consumption byvapor jet vacuum pumps without significantly degrading pump performance.

BACKGROUND OF THE INVENTION

[0002] Vapor jet pumps, also known as diffusion pumps, are widely usedfor vacuum pumping of enclosed chambers to high vacuum. The basiccomponents of a vapor jet pump include a generally cylindrical housinghaving an inlet at one end and a foreline. The foreline is typicallycoupled to a roughing pump and functions as an exhaust port. A boilerassembly is sealed within the other end of the housing. The boilerincludes a reservoir for a liquid, such as oil, and a heater forvaporizing the liquid. A jet assembly mounted within the housing directsone or more vapor jets toward the housing wall, where the vapor iscondensed. The condensed vapor returns to the liquid reservoir, and thecycle is repeated. The vapor jet drags the gas molecules from theenclosed chamber to which the pump is attached, thereby vacuum pumpingthe chamber. The vacuum chamber and the vapor jet pump may be part of aprocess control system.

[0003] Limiting power consumption is frequently an important issue inthe operation of process control systems and other equipment where vaporjet pumps are used. Most modern vapor jet pumps function at power inputas low as about one-third of the nominal specified power to the heater.The performance parameters usually change as follows. The maximumthroughput capacity and the maximum permissible discharge pressurereduce with a linear relationship to power. The maximum compressionratios reduce significantly more than that.

[0004] With regard to work done to compress the pumped gas, vapor jetpumps are very inefficient. At maximum throughput operation, theefficiency may be only 1 or 2%. Most energy is going into re-heating andre-evaporating the condensed oil vapor. Typically the pump will maintainhigh vacuum in a vacuum chamber at power as low as about 25%, when theboiling process continues and the liquid is kept at the boilingtemperature. In many applications where the compression ratios for lightgases are not important and required pumping throughputs are low, powercan be saved through operation at lower power.

[0005] A simple way of conserving power is to shut off the pumpovernight or over a weekend.

[0006] This requires a loss of about an hour to restore the normaloperation and at least a partial loss of vacuum level in the vacuumchamber.

[0007] Another way of conserving power is to switch some or all of theheater to a lower power. A product called Deltawatt included anelectrical switching box for pumps with multiple heaters. The switchingbox was manually controlled.

[0008] Some users attempt to control the operation of the vapor jet pumpby switching the power on and off while observing the temperature of theliquid in the boiler. This can work with good instrumentation andcareful synchronization of peak throughput demand in the process periodwith peak vapor production. The temperature change is very small,typically 1° C. This method is difficult because the timing must bevaried for each application and because distinguishing temperaturedifferences of 1° C. may be difficult.

[0009] Accordingly, there is a need for methods and apparatus forcontrolling power in vapor jet vacuum pumping systems withoutsignificantly degrading performance.

SUMMARY OF THE INVENTION

[0010] According to a first aspect of the invention, a vapor jet vacuumpumping system is provided. The vapor jet vacuum pumping systemcomprises a vapor jet pump having an inlet port, an exhaust port, a jetassembly and a boiler, the boiler including a heater, and a powercontroller for automatically controlling power supplied to the heater inresponse to at least one control parameter.

[0011] In some embodiments, the control parameter comprises a programmedsequence of power levels. In other embodiments, the power controller isconfigured for controlling power supplied to the heater in response to asensed pressure in a process chamber being pumped by the vapor jet pump.In further embodiments, the power controller is configured forcontrolling power supplied to the heater in response to control signalsfrom a process control system. In additional embodiments, the powercontroller is configured for controlling power supplied to the heater inresponse to a combination of control parameters.

[0012] In some embodiments, the power controller may be configured forcontrolling power supplied to the heater at one of two or more discretepower levels. In other embodiments, the power controller may beconfigured for controlling power supplied to the heater over acontinuous range of power levels. The heater may include two or moreheater sections, and the power controller may be configured forselectively energizing one or more of the heater sections.

[0013] The power controller may be configured for synchronizingincreased power input to the heater with increased load on the vapor jetpump. Preferably, the control parameter is representative of load on thevapor jet pump.

[0014] According to another aspect of the invention, a method isprovided for vacuum pumping of a process chamber. The method comprisesthe steps of vacuum pumping a process chamber with a vapor jet pumphaving a boiler including a heater, and automatically controlling powersupplied to the heater in response to at least one control parameterthat is representative of load on the vapor jet pump.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a better understanding of the present invention, reference ismade to the accompanying drawings, which are incorporated herein byreference and in which:

[0016]FIG. 1 is a cross-sectional view of a prior art vapor jet vacuumpump;

[0017]FIG. 2 is a block diagram of a process control systemincorporating a vapor jet vacuum pumping system in accordance with anembodiment of the invention;

[0018]FIG. 3A is a block diagram of an embodiment of a power controllerthat responds to a programmed sequence of power levels;

[0019]FIG. 3B is a timing diagram that illustrates an example of aprogrammed sequence of power levels;

[0020]FIG. 4A is a block diagram of an embodiment of a power controllerthat responds to a sensed pressure;

[0021]FIG. 4B is a graph of a first example of a control function thatdefines pump power as a function of sensed pressure;

[0022]FIG. 4C is a graph of a second example of a control function thatdefines pump power as a function of sensed pressure; and

[0023]FIG. 5 is a block diagram of an embodiment of a power controllerthat responds to one or more control signals from a process controlsystem.

DETAILED DESCRIPTION OF THE INVENTION

[0024] A cross-sectional diagram of an example of a prior art vaporjetvacuum pump is shown in FIG. 1. Major components of the vapor jet pumpinclude a housing 10, a boiler 12 and a jet assembly 14. The housing 10includes a generally cylindrical shell 20 which defines an interiorregion 22, and a foreline conduit 24, which defines a foreline 28. Aninlet 26 to interior region 22 is formed at one end of shell 20. A coldcap 27 mounted in inlet 26 suppresses overdivergent flow, as known inthe art. The boiler 12 is sealed to the opposite of end of shell 20. Thehousing 10 further includes cooling fins 30, which are spaced apart fromeach other and which have a generally annular shape, and an inlet flange32 for attachment of the pump to a vacuum chamber. A foreline conduit 24includes a foreline flange 34 for attachment to a suitable conduit.Foreline conduit 24 is typically attached to a roughing pump. A baffle36 located in foreline conduit 24 improves condensation and inhibitsloss of oil vapor passing through foreline 28.

[0025] The boiler 12 includes a boiler housing 40 having an end plate 42sealed to the end of shell 20 and a fin structure 44 that extendsupwardly from end plate 42 into interior region 22. The fin structuredefines a cylindrical compartment for mounting a heater 50. The boilerhousing 40 is positioned within a cylindrical wall 52 of jet assembly14. A liquid reservoir 54 is located between boiler housing 40 and thecylindrical wall 52 of jet assembly 14. A cylindrical shell 56 surroundsfin structure 44 and helps to control the temperature of fin structure44 during operation. The boiler 12 may be surrounded by insulation 58external to shell 20.

[0026] The jet assembly 14 has a generally cylindrical configurationwhich defines a central passage 60 that carries vapor from boiler 12 toa first annular pumping stage 62 and to a second annular pumping stage64. An ejector stage is formed by a nozzle 66 that passes through a wallof jet assembly 14 and is aligned with foreline 28.

[0027] In operation, a liquid, such as oil, in reservoir 54 is vaporizedby heater 50. The vapor passes upwardly through passage 60 to pumpingstages 62 and 64. Each of the pumping stages 62 and 64 has an annularopening which directs the vapor outwardly and downwardly in a generallyconical vapor jet. The vapor in each vapor jet is condensed by therelatively cool cylindrical outer shell 20, and the condensed vaporreturns to liquid reservoir 54. The vapor jets drag the gas moleculesfrom the vacuum chamber to which the pump is attached, thereby vacuumpumping the chamber. The pumped gas molecules are exhausted throughforeline 28. The upper portion of cylindrical shell 20 is typicallycooled by a cooling fan (not shown), which may be part of the vapor jetpump or may be part of the equipment in which the vapor jet pump isutilized. Water cooling is normally used for larger pumps.

[0028] A thermal switch 70, mounted on a block 72 that is integrallyformed with shell 20, maybe used indicate when the liquid is vaporizedand the pump is ready for operation. A second thermal switch (not shown)mounted on block 72 adjacent to thermal switch 70 may be used toindicate an abnormal temperature condition.

[0029] A block diagram of a process control system incorporating a vaporjet pumping system in accordance with an embodiment of the invention isshown in FIG. 2. A process chamber 110 is vacuum pumped by a vapor jetpump 112. The foreline of the vapor jet pump 112 is connected to aroughing pump 114. A process controller 116 controls a process inprocess chamber 110. A power controller 118 automatically controls thepower supplied to vapor jet pump 112 as described in detail below.

[0030] As shown in FIG. 2, power controller 118 supplies controlled pumppower to vapor jet pump 112. More particularly, power controller 118supplies controlled pump power to heater 50 (FIG. 1) of vapor jet pump112. The power controller 118 may receive control inputs from anexternal source, such as an operator or a host computer, from processcontroller 116, from a pressure sensor 120 in process chamber 110, orfrom a combination of these sources to control the power supplied tovapor jet pump 112. Power controller 118 controls the heater power forvapor jet pump 112 in response to at least one control parameter.Preferably, the control parameter is representative of the gas load onthe vapor jet pump 112. The control parameter permits the power to beincreased when the load is relatively high and permits the power to bedecreased when the load is relatively low. The control is automatic inresponse to the control parameter or parameters. Embodiments of thepower controller 118 with different control parameters are describedwith reference to FIGS. 3A, 3B, 4A, 4B, 4C and 5.

[0031] Referring to FIG. 3A, power controller 118 receives a programmedsequence of power levels as a function of time. The programmed sequencecan be provided by process controller 116 (FIG. 2) or by an externalsource and can be stored in power controller 118. The programmedsequence is based on knowledge of the probable load on vapor jet pump112 as a function of time during a specified process. It will beunderstood that the values of the programmed sequence, such as powerlevels and times, can be adjusted, or a new program sequence can beinput to power controller 118. Furthermore, power controller 118 maystore two or more programmed sequences of power levels, which correspondto different process conditions. Power controller 118 also receives astart signal to initiate the programmed sequence.

[0032] An example of a simple programmed sequence is shown in FIG. 3B,where pump power is plotted as a function of time. The sequence isinitiated at time To, and pump power changes are programmed to occur attimes T₁, T₂ and T₃. The example of FIG. 3B utilizes a number ofdiscrete pump power levels. This embodiment may be useful where theheater in the vapor jet pump 112 has several sections, one or more ofwhich may be energized. It will be understood that the number of powerlevels and the times at which the power levels change may be varied tosuit a particular application.

[0033] Referring to FIGS. 4A and 4B, power controller 118 controls powersupplied to vapor jet pump 112 in response to a sensed pressure. Asshown in FIG. 2, a pressure sensor 120 located in process chamber 110provides a pressure signal to power controller 118 that isrepresentative of the pressure in process chamber 110.

[0034] As illustrated in FIG. 4B, the power level supplied to the heaterof vapor jet pump 112 may be increased as the sensed pressure in processchamber 110 increases. The increased pressure is indicative of anincreased gas load on vaporjet pump 112. FIG. 4B illustrates anembodiment where the power level supplied to the heater in vapor jetpump 112 is a continuous function of the control parameter (sensedpressure) over a range of values. A time delay typically occurs betweena sensed pressure increase and an increase in pumping capacity as aresult of the increased power input. Accordingly, this approach, whenutilized alone, is most useful for applications that are not sensitiveto temporary pressure increases.

[0035] An embodiment of the power controller 118 wherein the pump powerlevel is a discrete function of sensed pressure is illustrated in FIG.4C. When the sensed pressure exceeds a pressure P₀, the pump powerincreases to a first level, and when the sensed pressure exceeds apressure P₁, the pump power increases to a second level higher than thefirst level. In the embodiment of FIG. 4C, the power level increases insteps at specified pressure levels.

[0036] Referring to FIG. 5, power controller 118 controls the powersupplied to vapor jet pump 112 in response to one or more controlsignals from process controller 116 (FIG. 2). The control signals fromprocess controller 116 may supply specific pump power levels to powercontroller 118 or may command an increase or decrease in pump powerlevel. The control signals are based on knowledge by process controller116 of the load likely to be imposed on vapor jet pump 112 during aparticular process or a step of a process.

[0037] In other embodiments, the power controller 118 may be configuredfor controlling the power supplied to vapor jet pump 112 in response tomore than one control parameter. In one embodiment, the power controller118 may control pump power in response to a programmed sequence of powerlevels and a sensed pressure level. Thus, for example, the powercontroller 118 may proceed according to the programmed sequence unlessthe sensed pressure exceeds a predetermined value. In this case, thesensed pressure overrides the programmed sequence and causes a pumppower increase to reduce the pressure in process chamber 110 to adesired level. In another embodiment, the power controller 118 maycontrol pump power in response to a programmed sequence and controlsignals from process controller 116. In this case, the power controlleroperates in accordance with the programmed sequence until a controlsignal is received from process controller 116. The control signal mayindicate, for example, that the power supplied to vapor jet pump 112 maybe reduced due to a delay in the process. It will be understood thatmany different control parameters and many different combinations ofcontrol parameters may be utilized within the scope of the invention. Ingeneral, the goal is to reduce the power consumption by vapor jet pump112 without significantly degrading performance.

[0038] The power controller 118 may include control circuitry forimplementing a desired control function in response to the controlparameter and may further include power components for controlling ACpower supplied to the heater of the vapor jet pump according to thecontrol function. For example, the power controller 118 may include aprogrammed microprocessor and triac power control devices, which arecontrolled by the microprocessor. The microprocessor is programmed toimplement a desired control function as a function of the controlparameter, as shown by way of example in FIGS. 3B, 4A and 4B. In thecase of a programmed sequence, the microprocessor stores the programmedsequence and controls the pump power in accordance with the sequence. Inthe case of an input control signal or sensed pressure, themicroprocessor controls the pump power in accordance with a programmedcontrol function.

[0039] Having described this invention in detail, those skilled in theart will appreciate that numerous modifications may be made of thisinvention without departing from its spirit. Therefore, it is notintended that the breadth of the invention be limited to the specificembodiment illustrated and described. Rather, the breadth of theinvention should be determined by the appended claims and theirequivalents.

What is claimed is:
 1. A vapor jet vacuum pumping system comprising: avapor jet pump having an inlet port, an exhaust port, a jet assembly andboiler, said boiler including a heater; and a power controller forautomatically controlling power supplied to said heater in response toat least one control parameter.
 2. The vapor jet vacuum pumping systemas defined in claim 1, wherein the control parameter comprises aprogrammed sequence of power levels.
 3. The vapor jet vacuum pumpingsystem as defined in claim 2, wherein the programmed sequence of powerlevels is adjustable.
 4. The vapor jet vacuum pumping system as definedin claim 1, wherein said power controller is configured for controllingpower supplied to said heater in response to a sensed pressure in aprocess chamber being pumped by said vapor jet pump.
 5. The vapor jetvacuum pumping system as defined in claim 1, wherein said powercontroller is configured for controlling power supplied to said heaterin response to control signals from a process control system.
 6. Thevapor jet vacuum pumping system as defined in claim 1, wherein saidpower controller is configured for controlling power supplied to saidheater in response to a combination of two or more control parameters.7. The vapor jet vacuum pumping system as defined in claim 1, whereinsaid power controller is configured for controlling power supplied tosaid heater at one of two or more discrete power levels.
 8. The vaporjet vacuum pumping system as defined in claim 1, wherein said powercontroller is configured for controlling power supplied to said heaterover a continuous range of power levels.
 9. The vapor jet vacuum pumpingsystem as defined in claim 1, wherein said heater includes two or moreheater sections and wherein said power controller is configured forselectively energizing one or more of said heater sections.
 10. Thevapor jet vacuum pumping system as defined in claim 1, wherein saidpower controller is configured for synchronizing increased power inputto said heater with increased load on said vapor jet pump.
 11. The vaporjet vacuum pumping system as defined in claim 1, wherein said controlparameter is representative of load on said vapor jet pump.
 12. A methodfor a vacuum pumping of a process chamber, comprising the steps of:vacuum pumping a process chamber with a vapor jet pump having a boilerincluding a heater; and automatically controlling power supplied to saidheater in response to at least one control parameter that isrepresentative of load on the vapor jet pump.
 13. The method as definedin claim 12, wherein the step of controlling power comprises controllingpower supplied to said heater in accordance with a programmed sequenceof power levels.
 14. The method as defined in claim 12, wherein the stepof controlling power comprises controlling power supplied to said heaterin response to sensed pressure in the process chamber.
 15. The method asdefined in claim 12, wherein the step of controlling power comprisescontrolling power supplied to said heater in response to control signalsfrom a process control system.
 16. The method as defined in claim 12,wherein the step of controlling power comprises controlling powersupplied to said heater in response to a combination of two or morecontrol parameters.
 17. The method as defined in claim 12, wherein thestep of controlling power comprises controlling power supplied to saidheater at one of two or more discrete power levels.
 18. The method asdefined in claim 12, wherein the step of controlling power comprisescontrolling power supplied to said heater over a continuous range ofpower levels.
 19. The method as defined in claim 12, wherein said heaterincludes two or more heater sections and wherein the step of controllingpower comprises energizing one or more of said heater sections.
 20. Amethod for controlling a vapor jet pump having an inlet port, an exhaustport, a jet assembly, and a boiler, said boiler including a heater, themethod comprising: automatically controlling power supplied to theheater in accordance with a control algorithm.